Application Information:

The PI2003 is designed to replace ORing diodes in

high

current

redundant

power

architectures.

Replacing a traditional diode with a PI2003

controller IC and a low on-state resistance N-

channel MOSFET will result in significant power

dissipation reduction as well as board space

reduction, efficiency improvement and additional

protection features. This section describes in detail

the procedure to follow when designing with the

PI2003 Active ORing controller and N-Channel

MOSFETs. The following is a low side Active ORing

design example.

Fault Indication:

FT

output pin is an open collector output and

should be pulled up to the logic voltage or to the

output can be pulled with a current limiting resistor

directly to an unregulated voltage source, such as

the return of a -48V bus. In this condition connect

opto-coupler device. The circuit in figure 12a shows

a PI2003 configuration for an LED/opto-coupler that

will turn on during a fault condition.

The FC

Use the circuit in figure 12b to turn on the LED/opto-

coupler when there is no fault and to turn off during

a fault condition.

Figure 12a: Fault circuit where the LED turns on

during a fault.

Figure 12b: Fault circuit where the LED turns off

during a fault.

VC Power Source:

The PI2003 VC input voltage should be higher than

the required gate-to-source voltage (Vgs) to fully

enhance the MOSFET. The maximum gate to VC

in the Gate Driver section under the

Electrical Specification.

If the bus voltage is higher than 11V then a bias

resistor (Rbias) is required, and should be

connected between the PI2003 VC pin and supply.

The resistor is selected based on the input voltage

range.

max

min

IC

VC

Vbus

Rbias

clamp

−

=

Rbias maximum power dissipation:

Rbias

VC

Vbus

Pd

clamp

Rbias

2

max

)

(

−

=

input voltage and minimum clamp voltage (11V).

Where:

min

Vbus

: V(bus) minimum voltage

max

Vbus

: V(bus) maximum voltage

Clamp

VC

: Controller clamp voltage, 11V

max

IC

: Controller maximum bias current (2.0mA)

)

during a fault condition should be added to

the maximum bias current

in the

above equations.

FT

I

max

IC

be

calculated

using

the

following

approximate equation:

FT

clampMax

FT

R

VC

I

=

N-Channel MOSFET Selection:

There are several factors that affect the MOSFET

selection

including

cost,

on-state

resistance

(Rds(on)), current rating, power dissipation, thermal

conductivity, drain-to-source breakdown voltage

(BVdss), gate-to-source voltage rating (Vgs), and

The first step is to select suitable MOSFETs based

on the BVdss requirement for the application. The

BVdss voltage rating should be higher than the

applied Vin voltage plus expected transient voltages.

Stray parasitic inductance in the circuit can also

contribute to significant transient voltage conditions,

particularly during MOSFET turn-off after a reverse

Picor Corporation • picorpower.com

PI2003

Rev 1.0